On average, a kindergarten teacher with more than 10 years on the job is worth an extra $1,100 per year to his or her students by the time they are earning a salary at age 27, the study shows. The lifetime gain for a class of 20 students with an above-average teacher totals $320,000 — and that's from a single year in a high-quality kindergarten class.

"We're not saying that teachers should be paid this much," said John Friedman, a faculty research fellow at the bureau and an economist at Harvard Kennedy School. "But very large amounts of money look like they might be worth it when it comes to finding better teachers."

Small classes make a difference, too: They are linked to higher test scores in kindergarten, which in turn improve a student's chances of attending college, the study shows. And regardless of race, gender or family income, students who learn more in kindergarten — or in any grade through third grade, for that matter — also are more likely to get into better colleges, marry, own homes, live in better neighborhoods and save for retirement by the time they turn 27, the economists found.

The results are surprising because previous research has shown that the impact of early grades on test scores fades out by eighth grade, said Raj Chetty, a research associate at the bureau and an economist at Harvard University.

"We found that everything comes back," he said. "Our paper shows that investments in early childhood education have potentially very large payoffs. In the U.S., kids from disadvantaged families attend lower quality schools because of property tax financing. That system basically perpetuates income inequality. Disadvantaged kids end up not doing so well. We should think about improving schools at the lower end of the school distribution."

The bureau study, conducted by Friedman, Chetty and a team of four other economists from Harvard, Northwestern University and the University of California, Berkeley, draws on data from Project STAR, one of the most widely studied education experiments in the United States. The project included 11,600 students and their teachers in kindergarten through third grade across 79 schools in Tennessee from 1985 to 1989.

Previous studies of STAR students have shown that those with more experienced teachers scored higher on standardized academic tests. The bureau economists for the first time found a similar impact on earnings in young adulthood. Based on the federal tax returns and W-2 forms of the former STAR students, they found that the students in the highest-earning kindergarten class were earning $1,520 per year more per student, on average, than their peers in the lowest-earning class. That's an extra $39,100 over a lifetime, or a lifetime gain of about $782,000 for a single class of 20 students.

"It gives you a sense of what's at play," Friedman said.

Numerous studies have highlighted the long-term benefits of Head Start and other intensive preschool programs. But the bureau study is the first to show on a large scale, using randomized data, that a better classroom environment in the earliest grades can have substantial benefits in adulthood, even without intervention in preschool.

Under the STAR project, the students were randomly assigned to less or more experienced teachers, either in small classes of between 13 and 17 students or in classes of 20 to 25 students. Most of the students stayed in the same size classes through third grade and took standard math and reading tests at the end of every grade. Thirty-six percent of participants were African-American. The students were less affluent, on the whole, than their peers nationwide: Sixty percent were eligible for free or reduced-price school lunches, compared to 49 percent of students in the same grades around the country.

In the bureau study, the economists tracked virtually all of the STAR children into early adulthood, looking at things like their income, college attendance, contributions to 401(k) retirement accounts, home ownership and marital status. They consulted U.S. News and World Report rankings to assess the quality of the colleges the students went to, and ZIP codes from the 2000 census to measure the quality of neighborhoods where they were living.

Why would the beneficial effects of good classrooms in the early grades fade out by eighth grade but re-emerge in adulthood? Perhaps the students in those classes are building skills such as focus, initiative and discipline, things that cannot be measured on academic tests but can pay off in other ways, the economists said. Previous studies have shown that students assigned to small classes in the early grades are more likely to complete high school and, in the case of white females and black males, less likely to give birth or father a child as teens.

"We don't see inside the classroom," Friedman said. "All we see is what happens on test scores. The positive effect works more through a teacher's ability to convey non-cognitive skills, like the ability to get along with your peers, pay attention in class and cooperate in groups. If you can share your toys with others, it's easy to see how you'd earn more, 20 years later in life."